The present invention is directed to the field of ignition systems, and, more particularly, to a capacitor discharge ignition (CDI) system capable of producing continuous ignition sparks of various durations.
Automotive ignition systems produce high voltage electrical discharges at the terminals of one or more spark plugs to ignite a compressed air fuel mixture. The electrical discharge is required to be produced when the piston is at a particular physical position inside the cylinder. The spark intensity should also be independent of the engine speed. Further, to optimize engine performance, improve fuel economy, and minimize polluting effluents, the time of occurrence and duration of the spark should be controllable in accordance with a predefined discharge profile.
There are primarily two types of ignition systems in use today, namely inductive ignition systems and capacitive discharge ignition (CDI) systems. In the inductive ignition system, the ignition voltage is generated by a sudden injection of current through the primary winding of the ignition coil. The main disadvantage of the inductive ignition system is that the ignition energy falls off at high engine speed.
In CDI systems, the ignition voltage is generated by discharging a charged capacitor through the primary ignition coil using an electronic switch. The capacitor is initially charged to a high voltage from a high voltage direct current (DC) source. At present, the CDI system is primarily used in two-wheeled vehicles to meet new emission standards and to offer improved fuel economy. Some variations of CDI systems are also used in cars and in certain racing applications.
Modern CDI systems typically use microcontrollers/microprocessors to provide engine parameter dependent ignition timings. To increase spark energy and provide better fuel combustion, some CDI systems also use intermittent multi-spark techniques. Several other improvements have been described in various U.S. patents. For example, U.S. Pat. No. 3,340,861 describes an inductive ignition system in which a ballast resistor is eliminated. However, this system still suffers from the limitations of inductive ignition systems at high engine speed. Moreover, U.S. Pat. Nos. 3,620,201; 3,658,044; and 3,838,328 describe various systems for producing multiple spark ignition in CDI systems. Yet, none of these systems are capable of producing continuous sparks or sparks of an extended duration.
Similarly, U.S. Pat. No. 4,228,778 describes a system for extending the spark duration in CDI systems. Even so, this system is also not capable of relatively long spark duration, as the capacitor needs time for charging between consecutive discharges. U.S. Pat. No. 4,738,239 outlines a system for enabling the use of power MOSFETS in inductive discharge systems, but this system does not offer any improvement in spark duration.
Other examples include U.S. Pat. Nos. 4,922,883 and 5,220,901, which define additional systems for providing multiple sparks and extended sparks in CDI systems, respectively. Even so, these systems are not capable of continuous sparks, nor can discharge time be controlled to achieve extended durations. Additionally, U.S. Pat. No. 6,167,875 provides an approach for adjusting the number of ignitions per cycle per cylinder depending upon the nature of the fuel-air mixture at low and high engine speeds. However, this approach is not capable of enabling continuous sparks of extended duration.
An object of the present invention is to provide an ignition system that can produce continuous ignition current for durations of various lengths.
This and other objects, features, and advantages in accordance with the present invention are provided by a capacitor discharge ignition (CDI) system capable of generating a continuous electrical discharge at a spark gap for a desired duration. The CDI system may include an ignition capacitor connected at one terminal thereof to a first terminal of the primary side of an ignition coil. At the other terminal, the ignition capacitor may be connected to an input terminal of a first controllable power switching means or circuit. The power switching circuit may also have an output connected to the common terminal of a high voltage DC source means or circuit which generates a stable high DC voltage. The primary side of the ignition coil also may have a second terminal connected to a common (i.e., ground) terminal.
Moreover, the CDI system may also include a controller connected to the control terminal of the first controllable power switching circuit, and a spark gap connected across the secondary side of the ignition coil. In addition, a second controllable power switching means or circuit may also be included with an input terminal connected to the output terminal of the high voltage DC source circuit, an output terminal connected to the input terminal of the first power switching circuit, and a control terminal connected to a second output of the controller. The first controllable power switching circuit may be used for discharging the discharge capacitor, and the second controllable power switching circuit causes charging of the discharge capacitor. This enables an ignition current through the ignition coil for any desired number of cycles during both the charge and discharge cycles of the discharge capacitor.
In particular, the high voltage DC source circuit may be a DCxe2x80x94DC converter that produces a stable high voltage DC output substantially independent of the variation in the voltage from the primary power source. Further, the first controllable power switching circuit and the second controllable power switching circuit may be electronic power switching devices, such as insulated gate bipolar transistors (IGBT), power MOSFETS, and power bipolar junction transistors (BJT). Additionally, the high-voltage DC source may also be an engine alternator.
The controller may be a microcontroller with a half-bridge driver for driving the controllable power switching circuit. The controller may also include a triggering control means or circuit for controlling ignition in accordance with a desired ignition profile. In particular, the triggering control circuit may control ignition in accordance with signals obtained from one or more sensors monitoring various parameters such as piston position, engine speed, throttle position, emission quality, type of fuel, etc.
By way of example, the triggering control circuit may include a data storage device including the triggering profile data, and it may determine desired triggering based on the triggering profile data. Furthermore, the triggering control circuit may include a signal processor for conditioning the signals received from the sensors. The ignition profile may define ignition occurrence and duration values with respect to various piston positions and engine speeds. Preferably, the ignition profile provides larger ignition duration during cold starting and at low speeds to produce fewer pollutants and ensure reliable operation. The CDI system may also therefore advantageously be applied to engines using alternative fuels requiring a long ignition duration.